Fixed antenna system for creating a rotational field



1954 CARL-ERIK GRANQVIST 3,

FIXED ANTENNA SYSTEM FOR CREATING A ROTATIONAL FIELD Filed March 4, 19584 Sheets-Sheet 1 FIG.I.

PRIOR ART STRUCTURE I I MOTOR/10 I l l I 1 souno coc I I 1 mscmmusm GEARl4 2| us souuo MECHANISM l7 \RADO rmzouzucv GENERATOR INVENTOR CARL-ERIKGRANQVIST Bygw wl ATTORNEY Oct. 13, 1964 CARL-ERIK GRANQVIST 3,153,233

FIXED ANTENNA SYSTEM FOR CREATING A ROTATIONAL FIELD Filed March 4, 19584 Sheets-Sheet 2 E/ /a 2 4 L i L 1 FIG.3

FIG.4.

FIG.5.

INVENTOR CARL-ERIK GRANQVIST I BY ATTORNEY Oct. 13, 1 6 CARL-ERIKGRANQVIST 3,153,233

FIXED ANTENNA SYSTEM FOR CREATING A RQTATIONAL FIELD Filed March 4, 19584 Sheets-Sheet 3 COMMUTATORx I SOUND MECHANISM I Q\ R. F. Generator if61 v MOTOR INVENTOR CARL- ERIK GRANQVIST BY 1 1 347A ATTORNEY Oct- 13, 1CARL-ERIK GRANQVIST 3,153,238

FIXED ANTENNA SYSTEM FOR CREATING A ROTATIONAL FIELD Filed March 4, 19584 Sheets-Sheet 4 INVENT OR CARL- ERIK GRANQVIST a ua/1 ATTORNEY UnitedStates Patent 3,153,238 FEED ANTENNA SYSTEM FOR CREATING A ROTATIUNALFIELD Carl-Erik Granqvist, Lidingo, Sweden, assignor t0 SvenskaAktieboiaget Gasaccumniator, Lidingo, Sweden, a corporation of SwedenFiled Mar. 4, 1958, Ser. No. 719,138 Claims priority, application SwedenSept. 4, 1957 4 Claims. (Cl. 343-106) For different purposes in radiotechnology, it is desirable to provide a rapidly rotating 'field havinga Very sharply limited directional characteristic. This is the case inwhich the transmitter antenna is used as a speaking radio beacon, whilethe receiver antenna is used in an automatic direction finding system. Adifiiculty in these antennas has been that one could not provide thedesired field rotation with the required constancy as far as regardsspeed without arranging all of the antenna system rotating in space.Centrifugal forces occur which were difficult to control, especially ifthe antenna system also was mounted in a place which was not protectedagainst the wind pressure, so that the forces occurring from the windpressure added themselves to the centrifugal forces. The mechanicalstrains were then, very often, so large that the antenna system couldnot afford them.

To these purely mechanical problems also some radiation electricalphenomena were added. Often the antenna system has been composed of twoor even more parts of antenna systems. In speaking radio beacons it hasbeen usual to provide a first antenna system for the purpose oftransmitting the bearing indication, and a second antenna system for thepurpose of transmitting, in the intervals between the times when a givenbearing indication was transmitted, a so-called covering field. Thecovering field drowns possible existing false bearing indications whichcould occur when signals in a direction which should not be audible arecaught by buildings, natural formations or the like in the vicinity andreflected. In receiver antennas for automatic direction finding systems,there has also been required an antenna in addition to the signalintercepting antenna, the purpose of which was to intercept the signaland rectify it for creating a control voltage for automatic volumecontrol.

In these antenna systems existing up to now, one always had to place theauxiliary antenna either to the side of the main antenna, above or belowthe main antenna. None of these possibilities has functioned well. Ifthe auxiliary antenna is placed at the side of the main antenna, thenone has to contend (1) with the possibility of an angular error betweenthe radiation characteristics of the two antennas, and (2) with the oneantenna working as a reflector for the other one and transmittingsignals in non-desired directions, and (3) with the relation between thefield intensities from the two antennas in different directions notbeing the same due to topographic conditions. If, on the other hand, theantennas are placed one above the other, then certainly the saiddisadvantages have been done away with, but instead one has to contendwith disturbing interferences by the ground reflection. In thisconnection, it is necessary to call to mind that here is the questionabout antennas for very short wave, as well as ultra short wave lengths,where the difference between the path of the direct wave and thegroundrefiected wave may very easily amount to half a wave length, sothat full interference with extinguishing of the signal will result. Aninvestigation proves that this state will take place along a conicalsurface with the point turned downward in the place Where the antennasystem is situated, and that the angle between the different generatrixlines of the conical surface and the ground will be larger, the higherup the antenna is placed. One has used this fact to decrease the riskfor signal extinguishing effect through interference of this kindby'intentionally building the antennas of said kind very low to theground. One has calculated that in such a case the extinguishing conecould be assumed to be so close to the'ground, that it would fallentirely within ranges where receivers of the signals transmitted fromthe said antenna, or transmitters of the signal to be received by thesaid antenna, respectively, will never be situated, and also thatbuildings, woods or the like would absorb the ground reflected wave,whereby the interference extinguishing effect could be avoided, or inany case decreased.

The application of the antenna mounted on a very low height meansdecreases the power of the antenna, which is not desirable. Therefore,there is a need to arrange a signal transmitting antenna or a signalreceiving antenna, respectively, in the same position of height as theauxiliary antenna.

The two problems mentioned above, that is, the provi sion of an antennafor a rotating field with sharply limited direction characteristicwithout said antenna having rotating parts, and the placing of saidantenna in such a way that the signal receiving or signal transmittingantenna, respectively, will be at the same height as the auxiliaryantenna, are solved by the present invention. This invention will befurther described below in connection with an embodiment including anantenna system for a speaking radio beacon.

The description of the invention will be made in connection with theattached drawings, in which: 7

FIGURE 1 shows a schematic diagram of the prior art structuralarrangement of the antenna system for a speaking radio beacon;

FIGURE 2 shows a corresponding arrangement of a plan View of the diagramaccording to the invention, containing dipoles, reflector bars, and aquarter of a wavelength commutator;

FIGURE 3 shows in vertical projection the arrangement of same dipolesand reflector bars.

FIGURES 4 and 5 show schematic wiring diagrams in abbreviated form for apart of the dipoles contained in the antenna system;

FIGURE 6 shows the radiation diagrams in the complete antenna systemaccording to the invention, when its dipoles are connected according toFIGURES 4 and 5; and

FIGURE 7 shows a wiring diagram illustrating how a signal generator isconnected to the dipoles of the antenna system.

The invention is described in connection with a transmitter antenna fora speaking radio beacon. It is obvious that it may be used with the sameadvantages in connection with any antenna intended to create a' rotatingfield diagram, and also that it can be used in connection With receiverantennas.

The known arrangement consists of a motor 10 driving the shaft 11together with the antenna 12 mounted thereon, said antenna beingcomposed of dipoles and intended to transmit bearing indications duringits rotation. The composition is of such a kind that the antenna willgive a' strongly limited directional field diagram, a so-calledcigar-formed diagram, containing the two lobes 13. For this purpose, themotor lll is also over a cog gear 14 connected to a tone machine. Amodulator 16 obtains its radio frequency current from a generator 17 andgives off current after modulation with the bearing indicationinformation to a commutator 18 and by means of this to theantenna 12.

Above the antenna 12 an auxiliaryantenna 19 is applied; This is also'ofthe dipole character, but its dipoles are arranged in such a way thatthe field transmitted will radiate according to the characteristics 20.It is seen from the drawing figure, that these characteristics form afigure similar to the figure 8 and have such a direction that the lobesof the characteristic 13 will fall generally in the angle between thetwo lobes of the characteristic 20. In any direction in relation to thespeaking radio beacon, one will therefore alternatively hear the signalfrom the antenna 12 during an angle of approximately 25 to 35, and thesignal from the antenna 19 during an angle of approximately 145 to 155thereafter with the same division of degrees again hear the signal fromthe antenna 12, and finally during the remaining part of the turn thesignal from the antenna 19.

As already mentioned, the signal from the antenna 12 is modulated with aspoken indication about the bearing on to the beacon at the moment whenthe listener hears this signal. In order to avoid that, the signal inquestion when it has another value is refiecte'd by means of objects inthe surroundings and erroneously being heard in the direction justmentioned. The signal from the antenna 19 is provided with a coveringtone, a so-called covering field, modulated on the same carrier wave.The carrier wave is also derived from the generator 17, but it ismodulated in a tone mechanism 21 with the signal of the covering fieldand by means of the commutator 18 transferred to the antenna 19.

It may now occur that a directly radiated wave 22 and a ground reflectedwave 23 from the antenna 19 meet at the observation point 24 with suchphase displacement (180) that the two waves extinguish each other or atleast substantially weaken the signal strength of the received signaland the purpose of the covering signal will no longer be fulfilled. Thisin the first place is depending upon the signal intensity from theantenna 19 having been so strongly decreased at the point 24 without thesignal intensity from the antenna 12 having been decreased in the samerelation. On the other hand it may occur that the signal intensity fromthe antenna 12 at another point will be decreased to a correspondingdegree or brought to zero value without the signal intensity from theantenna 19 being decreased to a corresponding degree. This lack inbalance between the signal intensities depends in its turn upon the twoantennas 12 and 19 being situated at different heights above ground.

According to the present invention the antenna itself is fixed and isthus not put into rotation. It consists of a number of dipoles 25(FIGURE 3), arranged in the form of a cage together with a correspondingnumber of grounded bars 26 being mutually connected. The number of barsare the same as the number of dipoles, or the double of this number orthe like, so that the grounded bars 26 form a screen. Each one of thedipoles in the antenna ring is connected with a fixed means in thecommutator 27 (FIGURE 2), whereas the corresponding means in thecommutator 27 are arranged to rotate in a way which will be furtherdescribed in the following.

For a more detailed explanation of the action of the antenna system, itis assumed that at a given moment the dipoles 2833 are connected to theconductor from the modulator 16 in a way shown in FIGURE 4. Regardingthe extraordinary short wave length of oscillations concerned, it isthereby important that the conduits to the different dipoles have thecorrect length. They are therefore combined to connection points 34, 35in immediate vicinity of the dipoles by means of conductors 36 11 ofadapted lengths, and the connection points 34 and 35 are in turncombined to a further connection point by means of exactly equally longconductors 42 and 43, respectively. The connection point 44, finally, isconnected to the tone machine and modulator 16 by means of a conductor45, the length of which is not critical.

The wave front corresponding to either one of the lobes 13 will now dueto its symmetry radiate in the direction 46, FIGURE 2. In order that thesame form of the characteristic shall be obtained, as in FIGURE 1, it istherefore desired to give the dipoles 30 and 31 a lag corresponding tothe radial distance A between the level through the dipoles 3G and 31and the level through the dipoles 29 and 32, whereas one is giving thedipoles 28 and 33 a lead of the value A equal to the radial distancebetween the dipoles 29 and 32 and the level through the dipoles 28 and33. If the number of dipoles is sufficiently great, then one can withallowable approximation regard A =A =A. If, on the other hand, thenumber of dipoles should be small, regard must be taken of theditterence betwen the two values. The said lead or the said lag,respectively, is provided by adaption of the lengths of the conduits 36,37' and 38 as well as, in a symmetrical sense, of the lengths of theconduits 41, 40 and 39. If, for instance, at a given moment, the phaseposition of the current to the dipole 29 should be equal to then byshortening the conduit 36, the phase position of the current to thedipole 28 is made equal to +A, and the phase position of the current tothe dipole 30 is madeequal to A by prolongation of the conduit 38.

The dipoles 47-52 (FIGURE 6), are symmetrically arranged andconsequently transmit a signal through the supplementary lobe 13. Thiscan be the same as the signal through the dipoles 23-33, but as a rule,it is advantageous to provide a separate modulator and tone mechanism,corresponding to the modulator and the tone mechanism 16 fortransmission through the-dipole system 47 52. Then it is possiblesimultaneously to transmit a given bearing indication through the onelobe 13, for in stance from the dipole system 28453, and an indicationof the contra bearing through the other lobe 13, in this case throughthe dipole system 4752.

In this case, the dipoles 53-58 together form something corresponding tothe antenna 19 in FIGURE 1. Regarding to begin with only the antennadipoles 54 and 57, these may be considered equivalent to the dipoles ofthe antenna 19. In the field direction 59, corresponding to the axialdirection of the field lobes 20, the radiation from the displaceddipoles 53 and 55 or 56 and 58, respectively, will support the radiationfrom middle dipoles 54 and 57, whereas the dissymmetry radiation in adirection perpendicular to the field direction 59 from the antenna 53 iscompensated for by the radiation from the antenna 55 turned in the samedirection. The corresponding will also have validity for the radiationfrom the antennas 56 and 58. One will therefore obtain a radiationdiagram from the antennas 53-58 which, with wholly allowable accuracy,will adapt itself to the radiation diagram 20, FIGURE 1. The coupling tothe antenna dipoles 53-58 will be evident from FIGURE 5. As a rule it isnot required to make any separate compensation of the lengths of thefeeder lines to the dipole antennas, but these feeder lines shouldsimply mutually be of equal length. The connection point 66 is connectedto the modulator and tone mechanism 21 by means of the commutator 18.

Practical tests have proved that a given length of the reflector bars isrequired in order to obtain a good screening action. Each dipole barshould, in the usual way, be of a length of 1/4, and the inward-turnedends should be rather close to each other, supported by a commoninsulator, and therefore the combined length will, as shown in FIGURE 3,be \/2. The reflector bars should not be less than %)t in length. Thedistance between each dipole element and the corresponding reflectorelement in radial direction should further be -)\/4. In all of the abovegiven dimension statements, A, as usual, indicates the wave length ofthe oscillation for which the antenna system is tuned.

When the commutator, connected to the antenna system according to theinvention, is placed into rotation, a successive switching will takeplace. Next after the described state, a state will occur in which thebearing indicating signal is connected to the antennas 29, 30, 31, 32,33, and 56, and on the other side to the antennas 51, 50, 49, 48, 47 and55, respectively. Simultaneously, the covering field signal is connectedto the dipole antennas 54, 53 and 28 or 57, 58 and 52, respectively.

The total picture of all of the field diagrams has turned one angularstep in a clockwise direction. It the total number of dipole elements iseighteen, as shown in the figures, this will correspond a turning of thefield diagram picture by 20. If the total number of dipole elementsshould instead be 27, the turning would be 15, and with 36 dipoleelements one would obtain a turning for each step of only FIGURE 6 showsa diagram for the characteristics in an antenna system according to theinvention at standstill. The dipoles have the same reference numerals asin FIGURES 2, 4 and 5. The characteristics of the bearing indicatingfield are drawn with heavy dash-lines, whereas the characteristics ofthe covering field are drawn by light dash-lines. One can see due to thespacings between the dipole units, there occur in the way well known tothe man skilled in the art, side lobes in connection with thecharacteristics of the bearing indicating field.

In FIGURE 6, the motor 62 drives the three sound mechanisms 16' and 16",corresponding to the sound mechanism 16 of FIGURE 1, and also the soundmechanism 21, corresponding to the sound mechanism 21 of FIGURE 1. Thesethree sound mechanisms are fed from the radio frequency generator 17,which also corresponds to the radio frequency generator 17 in FIGURE 1.

The dash-dotted lines are shown as the shaft 61 from the motor 62 to thedilferent sound mechanisms. In the conduits between the different soundmechanisms 16, 16" and 21, on the one side, and the antenna systemsbelonging thereto, on the other side, a commutator device 82, 83, 84 isshown and corresponds to the commutator 18 of FIGURE 1, but it is notmade in the same way as described in connection with FIGURES 3, 4 and 5,but instead it is constructed the way shown in FIGURE 7 by 67.

The connection between the modulator 16 and the dipole units 28-33 orthe dipole units entering in their place during the rotation of acommutator 67, is evident from FIGURE 7. The commutator is arranged on ashaft 61 driven by a motor 62 by means of a cog-gear 63 with a gearingrelation adapted in such a way that the tone mechanism will, at thecorrect moment, create the bearing indicating statements. The conductor64 is connected to the modulator 16. It is made in the form of a coaxialcable and over a pair of baluns 65, 66 for change to parallel conductorrelation connected to the stator portion of the capacitive commutator 67of a kind well known per se. The rotor portion of the commutator isconnected to a pair of baluns 68, 69 for changing the conductors intocoaxial relation, in which state they are carried on along the antennapole to distributors 78, 79 for connection to the difierent dipoleelements. The commutator is made as a qu-arter-wave-length coupling, theconduits of each from the baluns 68 and 69 being over collector points70, 71 and equalization lines 72, 73, 74 as well as 75, 76, 77,respectively, connected to primary bars of a quarter of a wavelength,said bars being grounded at their end turned away from the voltageconnection. In parallel with these bars, the primary bars, secondarybars are arranged which are also of a quarter of a wavelength. Theprimary bars are mounted on an insulating base connected to the shaft 61so that it will rotate together with this shaft, the secondary barsbeing fixed and connected to the dipole elements by means of baluns. Forinstance, the conductor 72 is over a primary bar 78 coupled to asecondary bar 79, said bar being by means of the conductor 80 and thebalun 81 connected to the dipole element 28.

The invention is, of course, not limited to the above describedarrangement, also shown in the figures, but different modifications mayoccur within the scope of the invention.

What is claimed is:

1. A speakingradio beacon comprising a first signal source fortransmitting signals for the indication of a bearing, and a secondsignal source for creating a covering signal, an antenna system having afirst radiation pattern in the shape of two sharply defined opposedbeams and a second radiation pattern in the shape of a figure 8 with theam's thereof perpendicular to the aXis of said beam, said antenna systemincluding a plurality of dipoles arranged at equal distances around acircle, a corresponding circle of reflector bars disposed inside saidcircle of dipoles, and a rotating commutator, having a stator and arotor portion, said stator portion connected to said dipoles and twomutually opposite groups of said rotor portion connected to said firstsignal source and two intermediate groups of said rotor portionconnected to said second signal source, whereby when some of saiddipoles are transmitting signals for the bearing indication within saidfirst radiation pattern the remainder of said dipoles are transmittingsaid covering signal within said second radiation pattern.

2. A speaking radio beacon according to claim 1, wherein said commutatorcomprises a plurality of quarter-wave-length couplings with theirprimary sides connected to said signal source and their secondary sidesconnected to said dipoles.

3. A speaking radio beacon according to claim 2 wherein said couplingsare connected to a plurality of common collector points by means ofintermediate conductors having a length adapted to compensate for thedistance between each dipole and a mean level for all of said dipolesacting in parallel.

4. A speaking radio beacon according to claim 1 wherein the number ofdipoles is a multiple of 9, one third of said dipoles being connected toa first transmitter for creating a first bearing identification signal,a diametrically opposite group of one third of said dipoles beingconnected to a second transmitter for creating a second bearingidentification signal, and the remainder of said dipoles being connectedto a third transmitter for creating a covering field in the shape of thesecond radiation pattern.

References Cited in the file of this patent UNITED STATES PATENTS2,188,649 Carter Jan. 30, 1940 2,407,169 Loughren Sept. 3, 19462,432,134 Bagnall Dec. 9, 1947 2,432,777 Luck Dec. 16, 1947 2,466,354Bagnall Apr. 5, 1949 ,0 8 Granqvist May 15, 1956 2,804,615 Wei'he Aug.27, 1957

1. A SPEAKING RADIO BEACON COMPRISING A FIRST SIGNAL SOURCE FORTRANSMITTING SIGNALS FOR THE INDICATION OF A BEARING, AND A SECONDSIGNAL SOURCE FOR CREATING A COVERING SIGNAL, AN ANTENNA SYSTEM HAVING AFIRST RADIATION PATTERN IN THE SHAPE OF TWO SHARPLY DEFINED OPPOSEDBEAMS AND A SECOND RADIATION PATTERN IN THE SHAPE OF A FIGURE 8 WITH THEAXIS THEREOF PERPENDICULAR TO THE AXIS OF SAID BEAM, SAID ANTENNA SYSTEMINCLUDING A PLURALITY OF DIPOLES ARRANGED AT EQUAL DISTANCES AROUND ACIRCLE, A CORRESPONDING CIRCLE OF REFLECTOR BARS DISPOSED INSIDE SAIDCIRCLE OF DIPOLES, AND A ROTATING COMMUTATOR, HAVING A STATOR AND AROTOR PORTION, SAID STATOR PORTION CONNECTED TO SAID DIPOLES AND TWOMUTUALLY OPPOSITE GROUPS OF SAID ROTOR PORTION CONNECTED TO SAID FIRSTSIGNAL SOURCE AND TWO INTERMEDIATE GROUPS OF SAID ROTOR PORTIONCONNECTED TO SAID SECOND SIGNAL SOURCE, WHEREBY WHEN SOME OF SAIDDIPOLES ARE TRANSMITTING SIGNALS FOR THE BEARING INDICATION WITHIN SAIDFIRST RADIATION PATTERN THE REMAINDER OF SAID DIPOLES ARE TRANSMITTINGSAID COVERING SIGNAL WITHIN SAID SECOND RADIATION PATTERN.